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From: graftonfot@yahoo.com (Mr. Land)
Newsgroups: sci.electronics.design,sci.electronics.repair,sci.electronics.misc,sci.electronics
Subject: Re: (Human) pulse pickup circuit contents?
Date: 17 Oct 2002 13:37:37 -0700
Organization: http://groups.google.com/
Message-ID: <3a81cd7b.0210171237.3003863d@posting.google.com>
References: <3a81cd7b.0210150928.c11d37d@posting.google.com> <3DAC6969.EFE9C9C6@imit.kth.se>
NNTP-Posting-Host: 204.166.190.3
NNTP-Posting-Date: 17 Oct 2002 20:37:37 GMT
Uwe Zimmermann wrote in message news:<3DAC6969.EFE9C9C6@imit.kth.se>...
>
> For those pickups from the hospital: they are a bit more complicated
> as they simultaneously measure the pulse and the oxygen concentration
> in the blood. They use two light sources (e.g. IR and red) which are
> alternatingly switched on and a photosensor measuring the reflected or
> transmitted intensity through your finger. Since the absorption of
> both wavelength depends on the optical density of the material in
> between (tissue and a varying amount of blood cells) while the ratio
> of the absorption at the two different main wavelengths depends on the
> color of the haemoglobin (and thus on the oxygen in the blood) these
> sensors can deliver both informations.
>
> In the case of your headband I would guess that it's just an IR
> reflection sensor, measuring the amount of IR radiation reflected from
> the blood cells in the blood vessels under your skin.
>
> Uwe.
Thanks. So I guess if I'm trying to determine which 2 of the 3
connections on the miniplug go to the sensor, I'd look for a high
resistance that changed as I covered/uncovered the window in the
headband? Thanks again.